Prior to setting forth the background of the invention, it may be helpful to set forth definitions of certain terms that will be used hereinafter.
The term “Wi-Fi” as used herein is defined as any wireless local area network (WLAN) products that are based on the Institute of Electrical and Electronics Engineers (IEEE) 802.11 standards.
The term “Access Point” or “AP” as used herein is defined as a device that allows wireless devices (also known as User Equipment or “UE”) to connect to a wired network using Wi-Fi, or related standards. The AP usually connects to a router (via a wired network) as a standalone device, but it can also be an integral component of the router itself.
The term “client” as used herein is defined as any device that has wireless communication capabilities, specifically, the IEEE 802.11 standards. A client may be for example a smart telephone, a laptop, a tablet or a personal computer (PC).
The notation “STA” as used herein is defined in as an IEEE 802.11 client.
The term “BSS” is an acronym for Basic Service Set, which is typically a cluster of stations supported by an AP.
The term “node” as used herein is defined as general name for both IEEE 802.11 AP and IEEE 802.11 STA.
The term “serving AP” as used herein is defined in relation to one AP and one STA, wherein the STA is registered to the AP, and the AP and STA are sending and receiving data to and from each other.
The term “neighboring APs” or “neighboring nodes” relate to two co-frequency (or co-channel) APs or nodes that are within each other's sensitivity range, e.g. at least one of them can receive the other in such an signal-to-noise ratio to allows decoding of signals.
The term “CCA range” as used herein is a range between two IEEE 802.11 nodes, wherein at least one node can receive the other's transmission at a power level equal or larger than “CCA Level” e.g. −82 dBm.
The term “CSMA/CA” stands for Carrier-Sense-Multiple-Access/Collision-Avoidance, representing a requirement to listen before transmitting in a multi-node wireless system that shares a common channel on the basis of first-come-first-served.
The term “preamble” as used herein describes a certain 802.11 transmitted signal modulation appearing at the beginning of each packet, that when received by other 802.11 nodes, will force them to yield channel access.
The notation “SINR” stands for Signal to Interference plus Noise Ratio.
The term “ACK” as used herein, stands for acknowledgement, and is defined as the signal transmitted from an IEEE 802.11 receiving node to the IEEE 802.11 node that has transmitted a packet to it, provided the packet was successfully received.
The term “time division duplex” (TDD) as used herein refers to systems using the same frequency spectrum for methods of communications in a time division manner such as Wi-Fi systems.
The term “channel sounding” or simply “sounding” is the process defined in 802.11 specifications that enables the full dimensionality of the radio channel to be determined. One sounding technique described in the 802.11 specifications is for an AP to transmit a Null Data Packet (NDP), a packet without a MAC frame.
The term “implicit channel sounding procedure” or simply “implicit sounding” is the process defined in 802.11 specifications, where both down and up links share the same spectrum. In the aforementioned process, the uplink channel estimated by the AP, is assumed to be identical to the downlink one—based on reciprocity principle—and is therefore is considered by the AP to represent the channel towards the client/STA. Specifically, an AP sends a request for a standard (known) sounding packet to the STA. In response, the STA sends the sounding packet and the AP estimates the uplink channel. The downlink channel is then assumed to be identical. As channel reciprocity is assumed, a calibration process is mandatory in implicit sounding.
The term “explicit channel sounding procedure” or simply “explicit sounding” is the process defined in 802.11 specifications where AP transmissions are channel estimated by the STA, and then fed back to the AP, providing it with the magnitude of phase and amplitude differences between the signals as transmitted by the AP vis-à-vis as received by the client/STA, allowing it to gauge or measure possible distortions and correct them.
Associated STA is defined herein as a STA that is served by a certain AP with a certain Service Set Identifier (SSID).
Non-associated STA is defined herein as a STA within the range of the non-serving AP.
The acronym “NAV” stands for Network-Allocation-Vector and represents virtual carrier sense mechanism, used by a Wi-Fi transmitting message to broadcast the predicted duration of its transmission, signaling to other nodes for how long 1 the channel be occupied.
The acronym “RTS” stands for Request-To-Send, and represents a message transmitted by one Wi-Fi node to another, probing it for information about its availability to receive data, per the Wi-Fi Alliance protocol.
The acronym “CTS” stands for Clear-To-Send, and represents a positive response from the other node to the node originating the RTS, indicating to the requesting node that the channel is clear from its point of view as well.
The notation “DURATION” is a message embedded in both RTS and CTS, representing a prediction of the future traffic about to be transmitted between two nodes that have captured the channel; other nodes that receive it, must clear the channel as long as the DURATION has not expired; other nodes that have received the RTS but received the CTS (hidden nodes) will avoid accessing the channel, allowing the receiving node to successfully complete the reception.
The acronym “FLA” stands for Fast Link Adaptation, and represents processes that reduce transmitting side learning time of the receiver's SINR.
The acronym “MCS” stands for Modulation Coding Scheme, mapping SINR to modulation order and code rate.
The acronym “MRQ” stands for MCS request (Modulation Code Scheme Request)
The acronym “MSI” stands for MRQ Sequence Identifier, which carries MCS feedback from receiver to transmitter.
The term “null” as used herein, is a spatial pattern, created by two or more antennas, formed in such a way that significantly reduces the power level received by a given receiver (e.g., a local minimum). An “Rx Null” is a null formed by a receiver's antennas weight in order to decrease undesired signal level. A “Tx Null” is formed by transmitter's antennas weights in order to decrease its undesired transmitted signal at remote receiver's input.
The term “actual null depth” as used herein, is the estimated value of the null after a certain time period has elapse since the last explicit sounding in which the amplitude and the phase have drifted so as to yield null degradation. The actual null depth is the original null taking account the estimated null degradation.
The term “AP Beacon” is a management signal that is transmitted at regular intervals (typically about 10 times per second) that indicates capability of the AP. The Beacon frame contains both mandatory information (such as SSID) and optional data that may include vendor specific information.
NDP represents Null Data Packet, transmitted by a Beamformer Node towards a Beamformee Node.
Compressed beamforming represents a data packet transmitted by a Beamformee Node towards a Beamformer Node as a response to a NDP; it comprised of a channel estimation matrix including all combinations of N Beamformee and M beamformer antennas.
Reciprocity calibration as defined herein is a process in which two TDD Nodes exchange transmissions, perform receptions, and calculate beamforming settings, so that the channel matrix values measured between the antennas of a first node and a second node in one direction, can be modified via said calibration process so that when used in the other direction, will be perceived by the other node with the same channel matrix values.
According to current IEEE 802.11 air protocols, two APs may download traffic over the same frequency channel to their respective STAs at the same time as long as these APs are not within CCA range of each other. When an RTS/CTS procedure is used, an additional condition is introduced, namely, a legacy STA receiving the download traffic from its serving AP, must not be within CCA range of other transmitting neighboring AP or STA.
It should be noted that the notations I, J, K given in capital letters, are not related to the notations i, j, k given in lower case.